1. Field of the Invention
The present invention relates to a safety mechanism for an open/close door member of an image forming apparatus such as a printer, a facsimile apparatus and the like.
2. Related Background Art
As an example of an equipment having an open/close member, a construction and a function of a laser beam printer using an electrophotographic process will be explained with reference to FIG. 10.
FIG. 10 is an elevational sectional view of the laser beam printer. In FIG. 10, the reference numeral 1 denotes a body of the printer; 2 denotes a cassette in which transfer sheets S are stacked; 21 denotes a sheet supply roller for picking up the transfer sheets S one by one from the cassette 2; 22 denotes a pair of regist rollers for controlling a convey timing of the transfer sheet S; 3 denotes a transfer charge roller; and 4 denotes a process cartridge. The process cartridge 4 incorporates therein at least a photosensitive drum 71, a developing device (not shown), a charger (not shown) a toner containing portion (not shown) and a cleaning device for the photosensitive drum as a cartridge unit which can detachably be mounted to the printer body 1.
A fixing device 5 includes a halogen heater 52, an aluminium fixing roller 51 and a rubber pressure roller 53. Developer on the transfer sheet S is fused by heat and pressure from the fixing roller 51 and the pressure roller 53 to be fixed to the transfer sheet S.
The reference numeral 23 denotes a pair of convey rollers; 24 denotes a pair of discharge rollers; 6 denotes a scanner unit for scanning the photosensitive drum 71 by reflecting a laser beam emitted from a laser generator (not shown) onto the photosensitive drum through a mirror 61; and 62 denotes a reflection mirror for directing the laser beam to the photosensitive drum 71.
Next, a printing operation will be described.
When a print signal is inputted from a host computer (not shown), the transfer sheet S is picked up from the cassette 2 by the sheet supply roller 21. The transfer sheet S is conveyed by the pair of regist rollers 22 at a timed relation to a tip end of a developed image on the photosensitive drum 71, and the developed image written on the photosensitive drum 71 by the laser beam and developed by the developing device is transferred onto the transfer sheet S by means of the transfer charge roller 3. The transfer sheet S to which the developed image was transferred is sent to the fixing device 5, where the developed image is fixed to the transfer sheet as mentioned above, and, then, the transfer sheet is conveyed and discharged by the pair of discharge roller 24.
In the above-mentioned laser beam printer, the process cartridge 4 is a consumed part, as well as the transfer sheet S. Further, an operator must dismount the process cartridge from the printer body if sheet jam occurs, in order to remove the jammed sheet.
In order to facilitate the replacement and mounting/dismounting of the process cartridge 4 effected by the operator, as shown in FIG. 11, the laser beam printer has an open/close door (referred to merely as "door" hereinafter) 7. The door 7 is closed to be positioned at a position X during the printing operation. However, when the process cartridge 4 is replaced or mounted or dismounted, the door is greatly opened to a position Y to facilitate the replacement and mounting/dismounting of the process cartridge 4.
However, the above-mentioned laser beam printer has the following disadvantage. That is to say, when the door 7 is opened to the position Y in FIG. 11 to perform the jam treatment, for example, if any shock acts on the printer body 1, the door 7 may be dropped from the position Y due to the shock to damage the printer body 1.
To avoid such inconvenience, the following countermeasures have been proposed:
(a) The door 7 is biased toward the position Y by using an elastic member to cancel the dropping force of the door 7;
(b) A stopping force providing "click feeling" is generated at the position Y to thereby prevent the dropping of the door 7; or
(c) The dropping force of the door 7 is weakened by providing a resist member generating a damper effect.
However, as the apparatus body has recently been made compact and light-weighted and personalized, since the arrangement of the apparatus is limited in order to improve operability, it is comprehended that the above-mentioned countermeasures cannot be adopted. For example, since outer members of the apparatus have relatively weak strength due to molded parts, if the biasing force is applied as the above item (a), the outer members will be deformed or creep will be generated in the outer members. Further, since the opening of the door is great, if the resist member generating the damper effect is provided in the vicinity of a fulcrum of the door as the above item (c), a damper generating a great force is required. The provision of such a damper is difficult in consideration of the installation space and, if such a damper is provided, the resistance force becomes great in comparison with the strength of the door, with the so that the fulcrum of the door may be damaged. Further, if there is a danger of applying a force exceeding the stopping force as the above item (b) to the door, the stopping force cannot eliminate the above inconvenience.
As mentioned above, if the problem regarding the dropping of the door cannot be solved by adding any function to the fulcrum of the door, any stopper is required to weaken the shock. However, in such a stopper, there arises a problem regarding the release of the stopper. That is to say, if the stopper is provided, when the operator tries to close the door, the door cannot be closed by the presence of the stopper. In this case, in order to release the stopper, the following two methods have been proposed:
(i) The door can be closed by overriding the click when the door is pushed with a strong force; and
(ii) After the stopper is manually released by the operator, the door is closed.
However, the operator cannot judge which method is used, resulting in an erroneous operation, or erroneously judges as the method (i) (although the method (ii) is actually adopted) to damage the stopper.
In order to eliminate such disadvantages, a stopper which is not operated by a normal operation and is operated only when a strong force is applied is required. To provide such a function, a mechanism of so-called "sheet belt type" is considered. However, since the sheet belt type cannot be judged a position where the function is operated, a "stopper responsive to only a shock force" is sometimes more effective.